As a conventional structure of a differential device of an automobile and a transfer device for four-wheel drive, a pinion shaft used in these devices is rotatably journaled via a skew contact double row ball bearing in which pitch circle diameters of double rows are different to each other, in other words, raceway diameters of the respective rows are different to each other. as is disclosed in Japanese laid-open patent application No. 2003-314541. The skew contact double row ball bearing of the foregoing type is called a tandem double row ball bearing.
The skew contact double row ball bearing incorporated in the differential device comprises, as shown in FIG. 6, an inner ring 113 having raceways 113a and 113b in double rows and externally fitted to a pinion shaft 107, an outer ring 111 having raceways 111a and 111b in double rows facing the raceways 113a and 113b of the inner ring 113 and internally fitted to a differential case 102, and double rows of balls 115 and 116 respectively interposed between the raceways 111a, 111b, 113a and 113b in the respective rows of the inner ring 113 and the outer ring 111. The double rows of balls 115 and 116 are respectively interposed between the raceways 111a, 111b, 113a and 113b with the different pitch circle diameters.
In the skew contact double row ball bearing, contact angles α1 and α2 of the respective rows may be different to each other, in which case, however, radial clearances of the respective rows in the skew contact double row ball bearing before the bearing is incorporated are equally set.